One thing is for certain: no matter how bad Gen 9 is, Gen 10 will be much worse because Pokemon's quality has been in a decline for a few years now. But how much worse will Gen 10 be?
Multiple Billy Eilish songs? A lesser number of gym leaders, maybe even one who just gives you the badge without any fight?
I think the next evolution of the dex cut will be individual mons being cut instead of entire evolution lines: for instance, maybe Mareep is in, but Ampharos isn't in the game in any form. And hey, maybe they'll cut a few types while they're at it?
I think Gen 10's "singer character who doesn't get voice acting" will actually be a singing guitar player who not only doesn't get voice acting but his guitar makes no noise when he strums on it in a cutscene. Shinyfags will be BTFO by a new item that can make any Pokemon shiny. That's funny, but there will also be a way to change your Pokemon's gender if not just outright assign them one.
As for glitches, Gen 10 manages to be so badly coded that it wipes your Pokemon file occasionally. We'll have to wait until Gen 11 before we get glitches to erase all save data on your Switch.
Where does the art style and character designs go from here? I can't imagine it being any worse, but I said that in Gen 8 and here we are in Gen 9 with mons and humans that are ugly in both their design and in art style. I will wager that there will 100% be at least one explicit MtF transexual portrayed positively in a role of importance. More outright homosexuality too.